THE ALIMENTARY CANAL AND ITS APPENDAGES § 171 
least conclude that, as a rule, the shorter appendices show 
occlusion more frequently than the longer (Ribbert). 
THE LIVER AND THE PANCREAS 
These two organs, which are genetically closely related, 
occasionally show variations in the manner of their lobation which 
may amount to constriction, and in the relations of their ducts. 
[Recent investigation at the hands of a number of independent 
workers has revealed the fact that the pancreas, in all classes of 
Vertebrates, is a compound organ, derivative of from one to four 
diverticula of the gut, and in most cases from three, as is said 
by Felix’ to be the case in Man himself. One (or more) of 
these primitive outgrowths gives rise to the chief duct (or ducts) of 
the adult organ, the rest usually becoming obliterated with advanc- 
ing development. Pending the working out of further details, 
considerable interest attaches to the recent discovery by Rolle- 
ston, that the duodenum of the human adult may sometimes 
bear a diverticulum (proved to be distinct from the “ampulla 
Vateri”) which enters the substance of the pancreas, and which 
there is reason to suspect may be a persistent vestige of one of 
the pancreatic outgrowths of the embryo.] 
The average weight of the liver is said to be 1451 gers. in 
the white races, 1266 ers. in the black. 
THE RESPIRATORY SYSTEM 
The visceral skeletal arches, which lie ventrad of the cranium 
proper and are intimately related to the cephalic portion of the 
gut, have been already mentioned in dealing with the head 
skeleton, and their great phylogenetic importance has been 
pointed out (cf. ante, pp. 49 and 64, and accompanying Figs.). 
A few additional remarks, however, are here necessary. 
Whereas certain Fishes (primitive Selachians) have from six 
to seven pairs of branchial pouches,’ Vertebrata somewhat higher 
in the scale (Turtles, Lizards, and Snakes) develop but five pairs, 
1 (Cf. Stohr, Anat. Anzieger, Bd. viii. p. 205.] 
2 (Jour. Anat. and Phys., vol. xxviii. p. xii.] 
* [It is insufficiently recognised that the “ Hag Fishes’ may bear many more than 
this, and that in one species of these (Bdellostoma polytrema) from thirteen to four- 
teen pairs are present (cf. Giinther, Brit. Mus. Cat. of Fishes, vol. viii. p. 512, 
and Schneider, Archiv f. Naturgesch., Bd. xlvi. p. 115.] 
